Re: [dpdk-dev] [RFC] hash: unify crc32 API header for x86 and ARM

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> 
> >> >> >> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
> >> >> >>
> >> >> >> Merge crc32 hash calculation public API headers for x86 and
> >ARM,
> >> >> >> split implementations of x86 and ARM into their respective
> >private
> >> >> >> headers.
> >> >> >> This reduces the ifdef code clutter while keeping current ABI
> >> >intact.
> >> >> >>
> >> >> >> Although we install `rte_crc_arm64.h` it is not used in any of the
> >lib
> >> >or
> >> >> >> drivers layers. All the libs and drivers use `rte_hash_crc.h` which
> >> >falls
> >> >> >> back to SW crc32 calculation for ARM platform.
> >> >> >>
> >> >> >> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
> >> >> >> ---
> >> >> >>
> >> >> >>  Currently, if application incorrectly sets CRC32_ARM64 as crc32
> >> >> >algorithm
> >> >> >>  through `rte_hash_crc_set_alg()` on x86 or vice-versa we
> >fallback
> >> >to
> >> >> >algorithm
> >> >> >>  set previously via `rte_hash_crc_set_alg()` instead of setting
> >the
> >> >best
> >> >> >>  available.
> >> >> >>  This behaviour should probably change to setting the best
> >> >available
> >> >> >algorithm
> >> >> >>  and is up for discussion.
> >> >> >>
> >> >> >>  app/test/test_hash.c            |   6 +
> >> >> >>  lib/librte_hash/Makefile        |   5 -
> >> >> >>  lib/librte_hash/crc_arm64.h     |  67 +++++++++++
> >> >> >>  lib/librte_hash/crc_x86.h       |  68 +++++++++++
> >> >> >>  lib/librte_hash/meson.build     |   3 +-
> >> >> >>  lib/librte_hash/rte_crc_arm64.h | 183 ------------------------------
> >> >> >>  lib/librte_hash/rte_hash_crc.h  | 193 +++++++++++++-----------
> >---
> >> >----
> >> >> >-
> >> >> >>  7 files changed, 219 insertions(+), 306 deletions(-)
> >> >> >>  create mode 100644 lib/librte_hash/crc_arm64.h
> >> >> >>  create mode 100644 lib/librte_hash/crc_x86.h
> >> >> >>  delete mode 100644 lib/librte_hash/rte_crc_arm64.h
> >> >> >>
> >> >> >> diff --git a/app/test/test_hash.c b/app/test/test_hash.c
> >> >> >> index afa3a1a3c..7bd457dac 100644
> >> >> >> --- a/app/test/test_hash.c
> >> >> >> +++ b/app/test/test_hash.c
> >> >> >> @@ -195,7 +195,13 @@ test_crc32_hash_alg_equiv(void)
> >> >> >>  	}
> >> >> >>
> >> >> >>  	/* Resetting to best available algorithm */
> >> >> >> +#if defined RTE_ARCH_X86
> >> >> >>  	rte_hash_crc_set_alg(CRC32_SSE42_x64);
> >> >> >> +#elif defined RTE_ARCH_ARM64
> >> >> >> +	rte_hash_crc_set_alg(CRC32_ARM64);
> >> >> >> +#else
> >> >> >> +	rte_hash_crc_set_alg(CRC32_SW);
> >> >> >> +#endif
> >> >> >>
> >> >> >>  	if (i == CRC32_ITERATIONS)
> >> >> >>  		return 0;
> >> >> >> diff --git a/lib/librte_hash/Makefile b/lib/librte_hash/Makefile
> >> >> >> index ec9f86499..f640afc42 100644
> >> >> >> --- a/lib/librte_hash/Makefile
> >> >> >> +++ b/lib/librte_hash/Makefile
> >> >> >> @@ -19,11 +19,6 @@ SRCS-$(CONFIG_RTE_LIBRTE_HASH) +=
> >> >> >rte_fbk_hash.c
> >> >> >>  # install this header file
> >> >> >>  SYMLINK-$(CONFIG_RTE_LIBRTE_HASH)-include := rte_hash.h
> >> >> >>  SYMLINK-$(CONFIG_RTE_LIBRTE_HASH)-include +=
> >> >rte_hash_crc.h
> >> >> >> -ifeq ($(CONFIG_RTE_ARCH_ARM64),y)
> >> >> >> -ifneq ($(findstring
> >RTE_MACHINE_CPUFLAG_CRC32,$(CFLAGS)),)
> >> >> >> -SYMLINK-$(CONFIG_RTE_LIBRTE_HASH)-include +=
> >> >rte_crc_arm64.h
> >> >> >> -endif
> >> >> >> -endif
> >> >> >>  SYMLINK-$(CONFIG_RTE_LIBRTE_HASH)-include +=
> >rte_jhash.h
> >> >> >>  SYMLINK-$(CONFIG_RTE_LIBRTE_HASH)-include +=
> >rte_thash.h
> >> >> >>  SYMLINK-$(CONFIG_RTE_LIBRTE_HASH)-include +=
> >> >rte_fbk_hash.h
> >> >> >> diff --git a/lib/librte_hash/crc_arm64.h
> >> >b/lib/librte_hash/crc_arm64.h
> >> >> >> new file mode 100644
> >> >> >> index 000000000..8e75f8297
> >> >> >
> >> >> >Wouldn't that break 'make  install T=...'?
> >> >>
> >> >> My bad I verified with meson and it was building fine.
> >> >>
> >> >> >As now rte_hash_crc.h includes not public headers (crc_x86.h,
> >etc.).
> >> >> >Same question about external apps, where they would get from
> >> >these
> >> >> >headers?
> >> >>
> >> >> I think in the next version we can directly have the arch specific
> >> >functions
> >> >> Implemented in rte_hash_crc.h. Since its pretty stable code and
> >> >overhead of extra
> >> >> ~120 lines.
> >> >
> >> >Ok... but why not then just leave arch specific headers, as they are
> >right
> >> >now?
> >> >What is wrong with current approach?
> >>
> >> The problem is if any application directly includes only
> >rte_crc_arm64.h
> >> (completely legal) it will break the build.
> >
> >But we can probably mark rte_crc_arm64.h as internal, and warn users
> >not to
> >include it directly (same for rte_crc_x86.h and any other arch specific
> >headers).
> 
> Yes but I think merging them would be a cleaner, number of constructors would be
> one and maybe we could select the best available algorithm on a given platform when
> application requests unsupported one.

Ok, but we can still have one constructor, and two (or more) different arch specific headers,
that would be included into main header conditionally by  #ifdef RTE_ARCH_....

> 
> As Yipeng mentioned do you thing having a indirect call instead of runtime branch be
> depreciative in terms of performance?

I think run-time branch by some global var would be much faster than indirect function call
(at least on IA).

> 
> >
> >>
> >> Example:
> >>
> >> diff --git a/lib/librte_efd/rte_efd.c b/lib/librte_efd/rte_efd.c
> >> index 6a799556d..318670940 100644
> >> --- a/lib/librte_efd/rte_efd.c
> >> +++ b/lib/librte_efd/rte_efd.c
> >> @@ -19,7 +19,7 @@
> >>  #include <rte_memcpy.h>
> >>  #include <rte_ring.h>
> >>  #include <rte_jhash.h>
> >> -#include <rte_hash_crc.h>
> >> +#include <rte_crc_arm64.h>
> >>  #include <rte_tailq.h>
> >>
> >>  #include "rte_efd.h"
> >> (END)
> >>
> >> Causes:
> >>
> >> ../lib/librte_hash/rte_crc_arm64.h: In function
> >'rte_hash_crc_set_alg':
> >> ../lib/librte_hash/rte_crc_arm64.h:77:7: error: 'CRC32_ARM64'
> >undeclared (first use in this function)
> >>    77 |  case CRC32_ARM64:
> >>       |       ^~~~~~~~~~~
> >> ../lib/librte_hash/rte_crc_arm64.h:77:7: note: each undeclared
> >identifier is reported only once for each function it appears in
> >> ../lib/librte_hash/rte_crc_arm64.h:79:10: error: 'CRC32_SW'
> >undeclared (first use in this function)
> >>    79 |    alg = CRC32_SW;
> >>       |          ^~~~~~~~
> >> ../lib/librte_hash/rte_crc_arm64.h:82:3: error: 'crc32_alg' undeclared
> >(first use in this function)
> >>    82 |   crc32_alg = alg;
> >>       |   ^~~~~~~~~
> >> ../lib/librte_hash/rte_crc_arm64.h: In function
> >'rte_hash_crc_init_alg':
> >> ../lib/librte_hash/rte_crc_arm64.h:92:23: error: 'CRC32_ARM64'
> >undeclared (first use in this function)
> >>    92 |  rte_hash_crc_set_alg(CRC32_ARM64);
> >>
> >> Thanks,
> >> Pavan.
> >>
> >>